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PPL Montana - Producing Power

Rainbow Dam
Generating capacity: 60 megawatts
336 Rainbow Dam Road,
Great Falls, MT 59404

The Rainbow Dam hydroelectric plant is located on the Missouri River, about 6 miles northeast of Great Falls, Mont. A new single-unit, 60-megawatt powerhouse was completed in early 2013, increasing the hydroelectric facility’s generating capacity by 70 percent. The new powerhouse replaces an eight-unit, 35-megawatt facility.

Rainbow began commercial operation in 1910. It was built to power the state’s growing mining industry at a time when mining companies were converting steam-driven machines to lower-cost electric motors. As the low cost electricity from Rainbow and other projects became available across the state, communities electrified.

Rainbow Dam is 1,055 feet long and 29 feet high. Its reservoir is 4 miles long. The dam is classified as a “run-of-river’ project because it can generate electricity using the water that flows down the river, without the need to store additional supplies. Immediately downstream from the dam is Rainbow Falls, which has a drop of 47 feet. Further downstream is Horseshoe Falls, with a drop of 12 feet.

PPL Montana broke ground on its $245 million Rainbow Redevelopment Project in October 2009. The new powerhouse began commercial operation April 22, 2013. The project created about 200 construction jobs and relied heavily on support from Montana businesses. The new turbine generates enough clean, renewable energy to power about 45,000 homes.

Water flows down a 2,500-foot power canal and through a 25-foot diameter penstock to the new turbine generator. The turbine’s slower rotation, wider flow passages and fewer rotating surfaces make it easier for fish to pass through unharmed.

Rainbow Dam is one of eight hydroelectric plants and one reservoir located along the Missouri and Madison Rivers and covered under PPL Montana’s Project 2188 operating license. Through this license, PPL Montana works with state and federal agencies and private groups to implement a diverse array of environmental stewardship projects to protect habitats on or near the banks of the Missouri and Madison Rivers.

Rainbow Dam is part of the Great Falls Portage National Historic Landmark. It is located between PPL Montana’s Black Eagle and Cochrane Dams. PPL Montana also operates the Ryan and Morony Dams on the Missouri River near Great Falls.

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